JP5230428B2 - Water-based treatment liquid for Sn-based plated steel sheet having excellent corrosion resistance and paint adhesion and method for producing surface-treated steel sheet - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention provides an aqueous treatment liquid for Sn-based plated steel sheet and a manufacturing method, which has excellent corrosion resistance and paint adhesion, and has been subjected to a surface treatment not containing hexavalent chromium as an automobile fuel tank material, household electric machine, or industrial machine material It is about .

  Conventionally, Pb-Sn-based plated steel sheets with excellent corrosion resistance, workability, solderability (weldability), etc. have long been used as automotive fuel tank materials, but their use has become difficult due to recent strengthening of environmental regulations for Pb. Yes. Various steel plates have been proposed as alternatives, but the application of Sn—Zn-plated steel plates is expanding because they are excellent in corrosion resistance, workability, and economy.

  JP-A-58-45396 and JP-A-5-106058 show a surface-treated steel sheet for a fuel tank in which a chromate treatment containing hexavalent chromium is performed on a Zn-Ni alloy plating. . Japanese Laid-Open Patent Publication No. 10-168581 and Japanese Laid-Open Patent Publication No. 11-217682 disclose a material obtained by chromate treatment of molten aluminum plating.

  However, the treatment method containing hexavalent chromium is excellent in corrosion resistance and economical efficiency, but since it is an environmentally hazardous substance, regulations are becoming strict and its use has been restricted. In order to solve this problem, a method of reducing hexavalent chromium disclosed in Japanese Patent Application Laid-Open No. 2006-028547 and a method using a Si-based chemical without using chromium are proposed in Japanese Patent Application Laid-Open No. 2001-32085. ing. However, depending on the corrosion resistance evaluation under severe conditions and the welding conditions, the conventional technology that does not contain chromium cannot sufficiently achieve the object. Furthermore, as shown in WO02 / 20874, a method using trivalent chromium having a low environmental load has been proposed. However, as described later, the prior art is a process invented based on a galvanized steel sheet. Even when applied directly to Sn-plated steel sheets having different surface states, the paint adhesion was insufficient.

  On the other hand, in the case of automotive fuel tank materials, Pb-Sn plated steel sheets called turn plating have been used. However, Pb may not be used due to European regulations, and molten aluminum plated steel sheets and molten Sn-Zn plated steel sheets are Has come to be used.

  In the prior art, methods for obtaining a processing solution having good liquid stability by combining trivalent chromium and an organic acid are disclosed in JP-A-10-81977, JP-A-10-81976, and JP-A-10-176279. JP-A-10-212586, JP-A-11-256354, JP-A-2001-181855, and JP-A-2002-146550, which show the amount of hexavalent chromium in the treatment liquid. The main focus is on reducing the amount of paint, and since the examination of the hydroxyl group / carboxyl group ratio in the organic acid molecule described later is insufficient, paint adhesion and water resistance are not necessarily sufficient. Similarly, Japanese Patent Application Laid-Open No. 2001-335958 is inferior in paint adhesion because an organic acid having an optimum hydroxyl group / carboxyl group ratio, which will be described later, has not been applied and no study has been made on improving paint adhesion. Although there is a description that silicate overcoat by two-step treatment is possible, water-soluble silicate is generally a salt with an alkali metal, and unlike water-dispersible silica, there is no effect of improving paint adhesion.

  In addition, the invention disclosed in Japanese Patent Application Laid-Open Nos. 2002-256447 and 2004-346360 is premised on water washing after coating and drying in addition to the above-described reason, and therefore, the amount of eluted components is large in the film components. It is inferior in paint adhesion. In the aforementioned Patent Document 6 and Japanese Patent Application Laid-Open No. 2002-226981, the paint adhesion is not studied. Since organic substances having a specific hydroxyl group are not included, and neither water-dispersible silica nor a combination of spherical silica and chain silica has been studied, it is inferior in alkali resistance and paint adhesion.

  The present invention is for solving the problems of the prior art described above, and is a hexavalent Cr-free aqueous treatment solution that is excellent in not only corrosion resistance but also paint adhesion, and a rust-proof treatment using the same. An object is to provide a Sn-based plated steel sheet.

As a result of intensive studies to solve the problems of the prior art, the present inventors have used a treatment liquid containing a hydroxycarboxylic acid having a specific structure, trivalent chromium, and water-dispersible silica. The present inventors have found that the above problems can be solved. That is, as a result of investigating the unfavorable cause of the paint adhesion of the Sn-based plated steel sheet, the main cause is the poor wettability of tin oxide (SnO, SnO ₂ ) formed on the plated surface during production or natural standing There was found. Therefore, as a result of diligent investigation, hydroxycarboxylic acids having a specific structure have improved adhesion between plating / film by forming a complex with Sn with a partial carboxylic acid group in the molecule, and other hydroxyl groups. It was clarified that good adhesion to paints can be secured because adhesion to paints can be secured. Here, Sn-based plating refers to plating in which the content (% by weight) of Sn in the plating layer is 20% or more. From 20% or more, the adverse effect on the paint adhesion due to the above-described tin oxide is developed. In addition, when the Sn content (% by weight) is 50% or more, the paint adhesion is further deteriorated, so that the improvement in paint adhesion due to complex formation with a carboxylic acid group becomes remarkable. If it is 80% or more, it becomes difficult to ensure adhesion of the paint, so that the effect of the present invention becomes more remarkable.

The present invention contains an organic substance (A), a water-soluble chromium compound (B), a water-dispersible silica (C) and water, and the organic substance (A) is at least one of ascorbic acid and its derivatives, Compound B) does not contain hexavalent chromium, and the dispersible silica (C) is composed of at least two types of spherical and chain, and the SiO ₂ weight ratio thereof is chain silica / spherical silica = 2/8 to It is an aqueous treatment solution for Sn-based plated steel sheet , having a pH of 8/2 and a pH of 1.0 to 6.0.

Further, phosphoric acid and / or phosphoric acid compound (D) is contained as an additional component of the aqueous processing liquid used in the present invention, and Cr and phosphoric acid and / or phosphoric acid compound (D) in the processing liquid of the present invention are contained. it is preferred that the total weight ratio of PO ₄ in the ranges of _{PO 4 / Cr = 1 / 1~3} / 1.

  Further, the aqueous treatment liquid used in the present invention contains a metal salt (E) as an additional component, and the metal is selected from the group consisting of Mg, Ca, Ba, Sr, Co, Ni, Zr, W, and Mo. It is preferable that the weight ratio of the metal and Cr is at least one of metal / Cr = 0.01 / 1 to 0.5 / 1.

The present invention is most achieved by applying the aqueous treatment liquid of the present invention to a steel sheet on which a Sn—Zn plating layer comprising 1 to 8.8 mass% Zn and 91.2 to 99.0 mass% Sn is formed and drying. Demonstrate the effect. Further, the aqueous treatment liquid of the present invention is applied to the Sn-based plated steel sheet and dried, and the dry film adhesion amount is 3 to 100 mg / m ² in terms of metal chromium per side, and Sn having excellent corrosion resistance and paint adhesion It is a manufacturing method of a system plating steel plate.

That is, the present invention contains an organic substance (A), a water-soluble chromium compound (B), a water-dispersible silica (C) and water, and the organic substance (A) is at least one of ascorbic acid and its derivatives. The chromium compound B) does not contain hexavalent chromium, and the dispersible silica (C) is composed of at least two types of spherical and chain, and the SiO ₂ weight ratio is chain silica / spherical silica = 2 / A water-based treatment liquid for Sn-plated surface-treated steel sheet having a pH of 8 to 8/2 and a pH of 1.0 to 6.0 , and the water-treated liquid applied to the surface of the Sn-plated steel sheet and dried. This is a method for producing a Sn-plated surface-treated steel sheet having excellent corrosion resistance and paint adhesion.

  As described above, the aqueous treatment liquid of the present invention does not substantially contain hexavalent chromium harmful to human body and environment, is excellent in liquid stability, and is applied and dried with the aqueous treatment liquid of the present invention. The Sn-based plated steel sheet manufactured in this way is excellent in both corrosion resistance and paint adhesion, and has a much greater environmental and industrial utility value than conventional fuel tank materials containing Pb.

The aqueous processing solution of the present invention will be described in detail below.
The aqueous treatment liquid of the present invention contains an organic substance (A), a water-soluble chromium compound (B), a water-dispersible silica (C) and water, and has a pH of 1.0 to 6.0. The organic substance (A) is at least one of ascorbic acid and its derivatives . Ascorbic acid has a hydroxyl group / carboxyl ratio of 5/1. When the ratio of hydroxyl group / carboxyl group is small , paint adhesion deteriorates with a decrease in the amount of coordination bond with Sn and deterioration of alkali elution resistance. When the ratio of hydroxyl group / carboxyl group is too large, the coating adhesion is deteriorated due to a decrease in the amount of coordination bond with Sn, and the aqueous treatment liquid is gelled or applied to the steel sheet surface due to an increase in viscosity. This is not preferable because the properties deteriorate.

Further, when the organic substance (A) has a smaller carbon number , the hydroxyl group / carboxyl group ratio is suitable, and none can be used industrially stably. If the carbon number is too large, the organic compound has a large number of hydrophobic groups, and the hydrophobic groups are unevenly distributed and aggregated during the formation of the film, so that cracks are likely to occur. As a result, coating adhesion tends to deteriorate, such being undesirable .

Specific examples include derivatives such as ascorbic acid and ascorbyl-2-glucoside.

The organic substance (A) used in the present invention is ascorbic acid and derivatives thereof, and is more likely to form a complex with Sn than an aromatic compound, and has excellent alkali resistance and thus tends to have excellent paint adhesion . Ascorbic acid is usually known as a lactone, but when the ring is opened, the ratio of hydroxyl group / carboxyl group becomes 5/1, the highest hydroxyl group ratio among sugar acids, and the most likely complex formation with Sn And since it is easily available industrially, it is most useful in the present invention. When the target plating is Zn-based, a complex with Zn should be formed, but since the atomic radius is different, the coordinating force is small as compared with the Sn complex, and the paint adhesion improving effect is small. Therefore, it can be said that the combination of Sn-based plating and ascorbic acid has a synergistic and effective effect.

  The compounding amount of the organic substance (A) used in the present invention is (A) / (B) = 0.01 to 0.80, preferably 0.03 in terms of a molar ratio of the water-soluble chromium compound (B) to Cr. It is -0.60, More preferably, it is 0.05-0.5. If it is less than 0.01, the paint adhesion improving effect is not observed, and if it exceeds 0.8, the water resistance of the resulting film is inferior, and in particular, the secondary adhesion with the coating film is lowered.

  The component (B) of the aqueous processing liquid of the present invention is a water-soluble chromium compound and substantially does not contain hexavalent chromium. The term “substantially free of hexavalent chromium” as used herein means that it is not detected by a colorimetric method using diphenylcarbazide, which is generally known as a quantitative method for hexavalent chromium. The aqueous treatment liquid of the present invention contains a chromium compound other than hexavalent chromium, and the liquid is colored by these. In order to reduce the influence of the coloring, the liquid was adjusted to 200 ppm with the total chromium concentration, and in the analysis result at this time, 0.1 ppm was regarded as the reliability limit, and less than 0.1 ppm did not contain hexavalent chromium. .

  The water-soluble chromium compound (B) may be any chromium compound that does not substantially contain hexavalent chromium as described above, and is not particularly limited. For example, chromium biphosphate, chromium fluoride, chromium nitrate And trivalent chromium compounds such as chromium sulfate. In addition, an aqueous solution containing hexavalent chromium ions in which chromic anhydride is dissolved in water is added to starch, sugars, alcohols, organic substances such as those shown in the organic substance (A) of the present invention, hydrogen peroxide, hydrazine, phosphorous acid. A compound obtained by adding a compound having a reducing action such as hypophosphorous acid and ferrous sulfate and reducing hexavalent chromium ions may also be used.

The component (C) of the aqueous processing liquid of the present invention comprises at least two kinds of spherical and chain , and the water dispersibility in which the SiO ₂ weight ratio is chain silica / spherical silica = 2/8 to 8/2 . Silica. As water-dispersible silica, for example, various types of Snowtex (registered trademark: manufactured by Nissan Chemical Industries, Ltd.) can be used. Although it does not specifically limit, for example, as Sphertex silica, Snowtex C, Snowtex CS, Snowtex CM, Snowtex O, Snowtex OS, Snowtex OM, Snowtex NS, Snowtex N, Snowtex NM, Snowtex S, SNOWTEX 20, SNOWTEX 30, SNOWTEX 40, etc., as chain silica, SNOWTEX UP, SNOWTEX OUP, SNOWTEX PS-S, SNOWTEX PS-SO, SNOWTEX PS-M, SNOWTEX PS-MO, Snowtex PS-L, Snowtex PS-LO, and the like can be mentioned. Dispersed vapor phase silica is not preferred because it tends to cause precipitation in the treatment liquid.

The mixing ratio of the component (C) in the aqueous treatment liquid of the present invention is preferably a weight ratio with respect to metal Cr in the water-soluble chromium compound (B), and SiO ₂ /Cr=0.5/1 to 6/1. If it is less than 0.5, the contribution to corrosion resistance and paint adhesion is small, and if it exceeds 6/1, the effect is saturated. The water-dispersible silica used in the aqueous treatment liquid of the present invention is more preferably used by mixing one or more of chain silica and spherical silica, and the ratio of chain silica / spherical silica is a weight ratio in terms of SiO _2. It is preferable that the chain silica / spherical silica = 8/2 to 2/8, and more preferably 6/4 to 4/6. If the weight ratio of chain silica / spherical silica exceeds 8/2, the alkali resistance tends to deteriorate, and if it is less than 2/8, paint adhesion cannot be sufficiently obtained.

The pH of the aqueous treating solution of the present invention is preferably in the range of 1.0 to 6.0, more preferably at 1.0 to 2.0. More preferably, it is 1.0-1.8. The acid added for adjusting the pH is not particularly limited, but strong acids that can adjust the pH with a small amount of addition are preferable, and examples thereof include nitric acid, sulfuric acid, and phosphoric acid. Examples of the alkali that raises the pH include ammonium salts such as ammonia and ammonium carbonate, amine compounds such as diethanolamine and triethylamine, and guanidyl compounds such as guanidine carbonate. When the pH of the aqueous processing solution of the present invention is less than 1.0 , the etching action on the plating becomes intense, and hydrogen generation occurs on the plating surface, resulting in poor processability. When the pH exceeds 6.0, the plating Sn surface is deteriorated. Oxide film removal is inadequate and liquid stability is reduced.

The aqueous treatment liquid of the present invention preferably contains phosphoric acid and / or a phosphoric acid compound as an additional component (D). These include, for example, orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, and their ammonium salts, amine salts, chromium biphosphate, and the like. Corrosion resistance is improved by including phosphoric acid and / or a phosphoric acid compound in the aqueous processing solution of the present invention. The phosphoric acid and / or phosphoric acid compound (D) is preferably in the range of PO ₄ / Cr = 1/1 to 3/1 in terms of mass ratio with respect to metal Cr in the water-soluble chromium compound (B). More preferably, it is the range of PO ₄ / Cr = 1/1 to 2/1. If it is less than 1/1, there is no effect of improving corrosion resistance, and if it exceeds 3/1, a decrease in paint adhesion is observed.

  The aqueous treatment liquid of the present invention preferably further contains a metal salt (E) as an additional component for the purpose of improving the corrosion resistance, and consists of Mg, Ca, Sr, Ba, Co, Ni, Zr, W, and Mo. It is preferable to contain at least one metal selected from the group. More preferably, the salt of Ni and / or Co is a metal-based weight ratio of metal / Cr = 0.01 / 1 to 0.5 / 1, more preferably the metal salt is a nitrate, and the metal / Cr = 0. .05 / 1 to 0.4 / 1. If it is less than 0.01 / 1, there is no effect of improving the corrosion resistance, and if it exceeds 0.5 / 1, the effect is saturated.

  In addition, phosphonic acid or a phosphonic acid compound can be added to the treatment liquid of the present invention in order to further improve the adhesion between the plating surface and the film. Although it does not specifically limit as a phosphonic acid compound, Methyl diphosphonate, a methylene phosphonate, ethylidene diphosphonate, etc., or these ammonium salts, alkali metal salts, etc. WHEREIN: A phosphonic acid group or its salt is 1 in a molecule | numerator. Examples of the oxidant include those having a nitrogen atom in the molecule thereof, which are oxidized to form an N-oxide.

  Moreover, a water-soluble resin can be mix | blended with this invention processing liquid as an additional component in order to improve corrosion resistance and coating property. The water-soluble resin is not particularly limited, but it is desirable to use a water-soluble acrylic resin or copolymer generally used for this purpose within a range not affecting the liquid stability.

  Further, examples of the plated steel sheet that is surface-treated with the treatment liquid of the present invention include tin, Sn alloy-plated steel sheets such as tin-plated steel sheets, electric Sn—Zn plated steel sheets, and molten Sn—Zn plated steel sheets. More preferably, it is a steel plate on which an Sn-based plating layer composed of 1 to 8.8% by mass of Zn and 91.2 to 99.0% by mass of Sn is formed. The purpose of adding Zn is to give sacrificial anticorrosive action to the plating layer. Tin-zinc alloy plating is based on zinc (standard potential: E0 = -1.245), which is a base metal, mainly protecting steel sheets with tin (standard potential: E0 = -0.14V) coating, which is an electrochemically noble metal. The sacrificial anticorrosive ability by V) is given. If the Zn content is less than 1% by mass, sufficient sacrificial anticorrosive ability cannot be obtained. When Zn exceeds the eutectic point of 8.8%, white rust is prominent, and this point is desirably set as the upper limit. The impurity element may be a trace amount of Fe, Ni, Co, Pb, or the like. Moreover, the effect of improving corrosion resistance can also be obtained by adding Mg. Further, if necessary, Al, misch metal, Sb, etc. may be added.

  The manufacturing method of the Sn-based plated steel sheet is not particularly defined, but the hot dipping method is preferable from the viewpoint that it is easy to obtain a thickening. As the hot dipping process, there are a Sendzimer method and a flux method, but a manufacturing method is not particularly limited. Further, in order to obtain a good appearance with Sn-based plating having a high Sn composition, it is preferable to perform Ni and Co-based pre-plating. This facilitates good plating without unplating. In particular, when Ni—Fe pre-plating is performed, an Sn dendrite structure that suppresses Zn concentration at the Sn-based plating spangle grain boundary is formed, and thus excellent corrosion resistance is obtained. At this time, a layer made of a Ni, Co, Fe plating layer, an Sn-based, Mg-containing intermetallic compound layer containing these, or a composite of both is formed at the interface between the Sn-based plating layer and the substrate. The thickness of this layer is not particularly limited, but is usually 1 μm or less.

The adhesion amount of Sn-based plating affects characteristics and manufacturing costs. Of course, it is preferable that the amount of adhesion is large for corrosion resistance, and that the amount of adhesion is small for spot weldability and cost. The amount of adhesion to balance is about 5 to 100 g / m ^{2 on} one side, and this range is preferable. For example, when the corrosion resistance of home appliances or the like is not required so much, the adhesion amount should be small, and it is desirable to use a large amount for automotive fuel tank applications where corrosion resistance is important.

The plated steel sheet is excellent in corrosion resistance with respect to the zinc-based plated steel sheet due to the coating of tin having excellent corrosion resistance. , SnO ₂ ) is brittle and has poor wettability, so that the adhesion between the plating and the paint was insufficient. However, the treatment liquid of the present invention creates a new surface of the plating metal by appropriately etching the tin oxide on the plating surface, and is an organic acid having a specific structure of Cr-silica-bonded directly to the plating metal after coating and drying. Therefore, a surface-treated Sn-based plated steel sheet having excellent corrosion resistance and excellent paint adhesion can be provided.

  About the processing method using the aqueous processing liquid of this invention, after apply | coating the aqueous processing liquid of this invention to the surface of plating steel materials, it should just heat-dry, and there is no restriction | limiting in particular about an application method, a drying method, etc. Usually, roll coating method in which the treatment liquid is applied by roll transfer to the surface of the material, or after the surface of the material is wetted by showering or dipping, the excess treatment liquid is removed with a roll squeezer or air knife to adjust the coating amount. Is mentioned. At this time, the temperature of the aqueous treatment liquid is not particularly limited, but the treatment temperature is preferably 5 to 60 ° C.

As for the drying temperature after apply | coating the aqueous processing liquid of this invention, it is desirable that it is 50-200 degreeC as the highest ultimate board temperature. The heating method is not particularly limited, and any method such as hot air, direct fire, induction heating, infrared, near infrared, and electric furnace may be used. Coating amount after drying is preferably from 3 to 100 mg / m ² in terms of weight of Cr, more preferably 4~80mg / m ^2, further preferably 5 to 40 mg / m ^2. If it is less than 3 mg / m ² , the effect of improving the corrosion resistance is poor, and if it exceeds 100 mg / m ² , cracks and the like are likely to occur in the coating itself, and the coating adhesion is lowered.

Next, the effect | action is demonstrated about the process liquid component of this invention.
As a result of detailed investigations by the inventors, the organic substance (A) of the present invention can be expected to have the following effects. First, it contributes to liquid stability as a processing liquid. Ascorbic acid and its derivatives are strongly coordinated to trivalent chromium ions with at least a pair of carboxyl groups and hydroxyl groups, and the remaining hydroxyl groups are hydrophilic. It is possible to suppress the condensation reaction and increase the stability of the treatment liquid. In addition, since ascorbic acid and its derivatives are selectively and strongly coordinated to Sn on the plating surface by at least a pair of carboxyl group and hydroxyl group, after coating and drying on the Sn-based plated steel sheet, It is possible to develop strong adhesiveness. In addition, coating corrosion resistance and paint adhesion by strengthening the bond with paint are improved by forming a film while forming a polymer by cross-linking with trivalent chromium and silica in combination.

  When the organic substance A is a chain like sugar acids, it is less susceptible to steric restrictions than a planar structure having an aromatic ring, which is advantageous for coordination to Sn. Furthermore, dehydration-condensation occurs in the bond in the film, and the covalent character is strengthened. Therefore, it is considered that the film has excellent water resistance and corrosion resistance.

  On the other hand, as an example of an organic substance having only a carboxyl group, for example, in the case of chromium acetate, liquid stability is ensured when the molar ratio of acetic acid / Cr (III) is 3 or more. In the treatment of plated steel sheets, it is considered that most of the carboxyl groups of acetic acid remain in the film even after coating and drying. In the film, the carboxyl group and Cr, or the plating metal are only electrostatically bonded, so the bond is likely to be broken by a local acid / alkali reaction in acid or alkali treatment or corrosion. Since the molecular weight is also small, it is easy to dissolve, so it is inferior in paint adhesion and corrosion resistance.

  Usually, polyacrylic acids are added for the purpose of improving the adhesion in the chromate film, but since polyacrylic acids are polymers, there are many bonding points in one molecule, and it is difficult to reach all of them. Therefore, the elution property is low and the above-mentioned weak points are unlikely to appear. However, since it easily crosslinks even in aqueous solution, depending on the amount added, the treatment liquid may gel, and even if it can be used for the purpose of improving paint adhesion with a small amount added, it is liquid stable as a counter ion for trivalent chromium. It cannot be used for the purpose of improving.

  Even in an organic substance having both a hydroxyl group and a carboxyl group, when the hydroxyl group / carboxyl group ratio is 2/1 or less, for example, lactic acid, tartaric acid, glyceric acid, citric acid, etc. For structural reasons, the coordinating power to Sn is lowered and disadvantageous in terms of alkali resistance, and paint adhesion is poor. On the other hand, when the hydroxyl group / carboxyl group ratio exceeds 10/1, the coordination power to Sn is lowered, so that the paint adhesion is lowered and the surplus hydroxyl groups interact three-dimensionally. The viscosity becomes higher and the applicability tends to deteriorate.

  The treatment liquid of the present invention requires water-dispersible silica (C), which can improve the corrosion resistance. Moreover, paint adhesion and alkali resistance can be made compatible by using two or more types of water-dispersible silica having different shapes. Since the water-dispersible silica has different effects on the film depending on the spherical and chain forms, it is preferable to mix two or more kinds in this way. Specifically, spherical silica is a spherical particle having a size of several nanometers to one hundred nanometers at a time. When a film is formed from the dispersion, it can be densely overlapped to form a smooth and small specific surface area film. On the other hand, chain silica is a particle in which spherical or ellipsoidal silica is connected in a chain of about several hundreds of nanometers. A film having a high specific surface area can be formed.

  Even when a chain silica was used for the treatment liquid of the present invention to form a film on the steel sheet surface, an uneven film was formed due to the effect of the chain silica, which was very effective in improving paint adhesion. However, when chain silica was used alone in the treatment liquid of the present invention, a decrease in alkali resistance was observed. The decrease in alkali resistance means that when the steel sheet of the present invention was washed with an alkaline solution (alkali degreasing), chromium as a film component was easily eluted. This phenomenon was found during the examination process of the present invention.

On the other hand, when spherical silica is used alone in the treatment liquid of the present invention, it is excellent in alkali resistance by forming a thin film with a small unevenness and a small specific surface area. Compared with silica, the paint adhesion decreased. That is, a film with few irregularities and a small specific surface area is excellent in alkali resistance, but is inferior in paint adhesion, and a film with many irregularities and a large specific surface area is inferior in alkali resistance, but is excellent in paint adhesion. Therefore, in the present invention, in order to achieve both paint adhesion and alkali resistance, one or more of chain silica and spherical silica are combined at a SiO ₂ weight ratio of chain silica / spherical silica = 2/8 to 8/2. It is preferable.

  The phosphoric acid or phosphate compound (D) of the treatment liquid of the present invention forms a three-dimensional insoluble salt with trivalent chromium after coating and drying, and is considered to be effective in improving corrosion resistance.

  The metal salt (E) of the treatment liquid of the present invention is effective in improving corrosion resistance in combination with silica. In particular, on the plating surface containing Zn, since the generation of basic zinc chloride or basic zinc carbonate that suppresses corrosion is promoted, the wear of zinc due to corrosion can be reduced.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, these Examples are described for description of this invention, and do not limit this invention at all.

[Preparation of test plate]
(1) Sample material
Preparation of molten Sn-based plated steel sheet Steels having the components shown in Table 1 are melted by a normal converter-vacuum degassing treatment to form a steel slab, followed by hot rolling, cold rolling, and continuous annealing processes under normal conditions. And an annealed steel plate (plate thickness 0.8 mm) was obtained. After applying 0.2 g / m ² of Fe—Ni plating to a part of this steel plate, Sn plating was performed by a flux method. The Fe—Ni alloy plating bath used was a nickel plating watt bath with 30 to 200 g / L of iron sulfate added. As the flux, a ZnCl ₂ aqueous solution was applied by roll coating, and the Zn composition in the plating bath was changed from 0 to 20 wt%. The bath temperature was 280 ° C., and the amount of plating was adjusted by gas wiping after plating. The plated steel sheet thus produced was temper-rolled with rolls having various roughnesses to adjust the surface roughness.

Preparation of hot -dip Zn-based plated steel sheet In the same manner as in the preparation example of hot-dip Sn-based plated steel sheet, the steels having the components shown in Table 1 were melted by a normal converter-vacuum degassing treatment to obtain a steel slab, followed by normal conditions. The steel sheet was hot-rolled and pickled in 10% hydrochloric acid, and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.8 mm. This cold-rolled steel sheet was annealed at a soaking temperature of 800 ° C. and a soaking time of 20 seconds using a continuous hot dipping equipment, cooled to 465 ° C. at a cooling rate of 20 ° C./sec, and then Zn-0 having a bath temperature of 460 ° C. It was immersed in a 2% Al plating bath for 3 seconds, and adjusted so that the amount of adhesion was 40 to 50 g / m ² by wiping.

  Several types of post-treatments were applied to this steel plate. Table 2 shows the types and compositions of post-treatments.

In addition, all the post-processing films were the same treatment on both sides. An annealed steel plate (plate thickness 0.8 mm) similar to the above was used as a comparative turn sheet. A portion of this steel plate was Ni-plated with a watt bath at 1 g / m ² and then Pb—Sn plated by a flux method. The flux was used by applying a ZnCl ₂ aqueous solution in a roll, and the Sn composition was 8%. The bath temperature was set to 350 ° C., and the amount of plating adhered was adjusted by gas wiping after plating, and then immersed in a 10 g / L phosphoric acid solution was used for the test.

(2) Degreasing treatment Each test material prepared above was degreased (fine concentration 20 g / L, temperature 60 ° C., 20 seconds) with a silicate alkaline degreasing agent Fine Cleaner 4336 (registered trademark: manufactured by Nihon Parkerizing Co., Ltd.). After spraying, it was washed with tap water.

(3) Preparation of surface treatment solution of the present invention Table 2 shows organic substances, Table 3 shows water-soluble chromium compounds, Table 4 shows water-dispersible silica, Table 5 shows phosphoric acid and its compounds, and Table 6 shows. Indicates a metal nitrate. Example No. shown in Table 7 4 to 33, Comparative Example No. 34-49 (except comparative example No. 42-43) has confirmed that hexavalent chromium is not included substantially. 30% reduced chromium is obtained by dissolving chromic anhydride in pure water and adding methanol to reduce 30% of hexavalent chromium. Further, 100% reduced chromium is added to this 30% reduced chromium so as to have the composition shown in Table 7 (water-dispersible silica is added later), and the pH is adjusted with nitric acid and aqueous ammonia, Hydrazine monohydrate (NH ₂ NH ₂ .H ₂ O) is added until hexavalent chromium is not detected.

  Each was mixed and dissolved so as to have the composition shown in Table 7, and the pH was adjusted using nitric acid and aqueous ammonia. Water-dispersible silica was added after adjusting the pH, and adjusted with pure water so that the Cr concentration was 1% by weight to obtain an aqueous processing solution.

(4) Application of surface treatment liquid Each of the surface treatment liquids prepared above was applied onto each test plate with a bar coater and dried at an ambient temperature of 240 ° C. The adhesion amount was adjusted by appropriately adjusting the solid content concentration of the surface treatment liquid, and the Cr adhesion amount (mg / m ² ) was measured using an average value in the Φ30 mm area by fluorescent X-ray analysis.

[Performance evaluation items and evaluation methods]
(1) Corrosion resistance test (planar surface corrosion resistance test)
A salt spray test according to JIS-Z-2371 was conducted for 1000 hours, the area where red rust was generated was observed, and evaluation was performed according to the following criteria.

〔Evaluation criteria〕
◎: Red rust generation area ratio is less than 3% of the total area ○: Red rust generation area ratio is 3% or more and less than 10% of the total area △: Red rust generation area ratio is 10% or more and less than 30% of the total area ×: Red rust generation area Rate is 30% or more of the total area

(2) Weldability Spot welding was performed under the weldability conditions shown below, and the number of consecutive hit points up to the point when the nugget system cut 4√t was evaluated.

[Welding conditions]
Electrode: Domed electrode, tip diameter 6 mm
Welding current: 95% of the current generated by dust
Applied pressure: 200kg
Pre-pressurization: 50 cycles Energization: 10 cycles Hold: 3 cycles

〔Evaluation criteria〕
A: Over 300 consecutive hit points ○: Continuous hit points 200-300 points Δ: Continuous hit points 100-200 points ×: Continuous hit points less than 100 points

(3) Paint adhesion The phthalic acid resin-based paint was applied to the test piece using a bar coater and dried by heating at 120 ° C. for 20 minutes to obtain a dry film thickness of 20 μm. Subsequently, it was immersed in boiling water for 30 minutes, taken out and allowed to stand naturally for 24 hours. Thereafter, a grid pattern of 1 mm and 100 squares was applied using a cutter knife, and the number of remaining coating films was determined by a tape peeling test. The evaluation criteria for paint adhesion are shown below. The number of individuals in the test was 2.

〔Evaluation criteria〕
◎: Remaining number 100 ○: Remaining number 98 to less than 100 △: Remaining number 50 to less than 98 ×: Remaining number less than 50

(4) Stability of treatment liquid Each aqueous treatment liquid was kept at 30 ° C. in a sealed state. The evaluation criteria for treatment liquid stability are shown below.
〔Evaluation criteria〕
◎: No gelation for 5 days or more ○: No gelation for 24 hours or more to less than 5 days Δ: No gelation for 1 hour or more to less than 24 hours × Gelation in less than 1 hour

(5) Long-term liquid stability 2 g / L of zinc carbonate in terms of Zn was added to each aqueous treatment liquid and kept sealed at 40 ° C. for 1 week. A sample in which gelation or precipitation was not observed in the treatment liquid was evaluated with a symbol ◯, and a sample that was recognized was evaluated with ×.

(6) Alkali Resistance After degreasing treatment (concentration 20 g / L, temperature 60 ° C., spraying for 20 seconds) with silicate-based alkaline degreasing agent Fine Cleaner 4336 (registered trademark: manufactured by Nihon Parkerizing Co., Ltd.), washing with tap water And dried in an oven at 80 ° C. for 10 minutes. The amount of Cr deposited before and after degreasing was measured by XRF, and the Cr fixation rate was calculated from the amount of Cr deposited after degreasing / the amount of Cr deposited before degreasing. The evaluation criteria of Cr fixation rate are shown below.

〔Evaluation criteria〕
A: Fixed rate of 98 to 100%
○: Fixed rate 90 to 98%
Δ: Fixed rate 50 to 90%
X: Fixed rate less than 50%

  As is clear from Table 7 and Table 8, the aqueous treatment liquid of the present invention is excellent in liquid stability, and the molten Sn-based plated steel sheet produced by applying and drying the aqueous treatment liquid of the present invention has excellent corrosion resistance. It had paint adhesion, weldability, and alkali resistance. On the other hand, as shown in Tables 7 and 8, the comparative example cannot obtain them in a well-balanced manner. The molten Sn-based plated steel sheets produced by applying and drying the aqueous treatment liquids shown in 42 and 43 had the same effects as the examples as shown in Table 8, but contained hexavalent chromium. Therefore, it is not an environmentally happy thing.

Claims (5)

The organic substance (A), the water-soluble chromium compound (B), the water-dispersible silica (C) and water are contained, and the organic substance (A) is at least one of ascorbic acid and its derivatives. Does not contain hexavalent chromium, and the dispersible silica (C) is composed of at least two types of spherical and chain, and the SiO ₂ weight ratio is chain silica / spherical silica = 2/8 to 8/2. Yes, an aqueous treatment solution for Sn-based plated steel sheet , wherein the pH is 1.0 to 6.0. As an additional component, phosphoric acid and / or phosphoric acid compound (D) is contained, and the mass ratio of Cr in the treatment liquid of the present invention to PO ₄ in phosphoric acid and / or phosphoric acid compound (D) is PO ₄ / Cr. The aqueous treatment solution for Sn-based plated steel sheet according to claim 1 , wherein the aqueous treatment solution is in a range of = 1/1 to 3/1. The metal salt (E) is contained as an additional component, and the metal is at least one selected from the group consisting of Mg, Ca, Ba, Sr, Co, Ni, Zr, W, and Mo, and the weight of the metal and Cr The ratio is in a range of metal / Cr = 0.01 / 1 to 0.5 / 1 , the aqueous treatment solution for Sn-based plated steel sheets according to claim 1 or 2 . The aqueous treatment liquid according to any one of claims 1 to 3 is applied to a steel sheet on which an Sn-based plating layer composed of 1 to 8.8 mass% Zn and 91.2 to 99.0 mass% Sn is formed. A method for producing an Sn-based plated steel sheet having excellent corrosion resistance and paint adhesion, characterized by being dried. According to claim 4, Sn having coating, corrosion resistance dry dry film coating weight is superior to being a 3 to 100 mg / m ² on one surface per reckoned as metal chromium of the Sn-based plated steel sheet, the paint adhesion Manufacturing method of a galvanized steel sheet.